While the cookies are cooling, make the peanut butter filling. In an
electric mixer fitted with the paddle attachment, beat cream cheese and
confectioner's sugar together until pale and fluffy. Add in salt,
peanut butter & vanilla and mix until combined.

To
assemble the cookie sandwiches, spread a generous dollop of peanut
butter filling on the underside of one brownie cookie and place a
second brownie cookie bottom side down on top. Cookies can keep be
stored chilled in an airtight container.